Hello, On 12/02/2009 01:01 AM, Ingo Molnar wrote: >>> The problem is that on UP configurations. Percpu memory allocator >>> becomes a simple wrapper around kmalloc and there's no way to >>> specify larger alignment when requesting memory from kmalloc. >> >> There is usually no point in aligning in UP. Alignment is typically >> done for smp configurations to limit cache line bouncing and control >> cache line use/ > > There is a natural minimum alignment for UP and it's smaller than the > cache-line size: machine word size. All our allocators (except bootmem) > align to machine word so there's no need to specify this explicitly. > > Larger alignment than that just wastes memory - which waste UP systems > can afford the least. This isn't usual alignment. struct work_struct has one data fields which is overloaded for two purposes. Lower few bits are used to carry flags while upper bits are used to point to sruct cpu_workqueue_struct. So, the number of available bits for flags are determined by the alignment of cpu_workqueue_struct. Memory usage for cwqs isn't a big concern here. Many workqueues will go away. I think we'll end up with less than half of what we have today while we'll continue to have large number of works. I'll just create alloc_cwq function which forces the alignment on UP. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
